The present invention relates to a method of bonding end portions of a flame retardant sheet consisting of a flame retardant layer sandwiched between resinous layers, the flame retardant layer being made of a flame retardant agent having extinguishability.
The invention also relates to a method of fabricating an intermediate transfer member by making use of the above-described bonding method, the medium being used in an image forming apparatus for forming an image using an electrophotographic technique such as a printer, facsimile machine, copier, or the like.
Generally, an image forming apparatus using an electrophotographic technique comprises: an image carrier having a photosensitive layer on its outer surface; a charger for uniformly charging the outer surface of the image carrier; an exposer for selectively exposing the outer surface uniformly charged by the charger to form an electrostatic latent image; a developer for applying toner (developer agent) to the electrostatic latent image formed by the exposer to thereby form a visible toner image, and a transferer for transferring the toner image developed by the developer to a recording medium such as paper.
An intermediate transfer member such as an intermediate transfer belt is known as the transferee. In particular, a toner image formed on the image carrier is transferred (primary transfer) and is further transferred (secondary transfer) to the recording medium.
Japanese Patent Publication No. 11-282260A discloses an intermediate transfer member formed in an endless manner. Specifically, a substrate sheet made of a resin is prepared, a conductive layer and a resistive layer are formed on one surface of the substrate sheet. End faces of the substrate sheet are placed opposite to each other with a space between them. A welding member is inserted into the space and abutted against the respective end faces. The welding member is melted using a welding tool such as an ultrasonic hone to weld together the end faces of the sheet.
In spite of the fact that a high-voltage transfer bias is applied to the intermediate transfer member, it is flammable because the substrate sheet is made of a resin. The above intermediate transfer member has only a flame retardant class of less than UL 94 VTM-2.
Therefore, in the past, when the intermediate transfer member is mounted in an image forming apparatus, the whole intermediate transfer member is covered by a cover having non-flammability. Accordingly, a large mounting space is necessary.
On the other hand, a sheet having a flame retardant layer having extinguishability (having the property of depriving oxygen) and sandwiched between resinous layers is known. Accordingly, if this sheet can be used as the substrate sheet of the intermediate transfer member, a flame retardant intermediate transfer member can be obtained. However, a flame retardant agent having extinguishability has no adhesiveness.
For this reason, an endless intermediate transfer member cannot be obtained by the method described in the above publication because the flame retardant agent around the joint hinders welding between the resinous layers, thus deteriorating the bonding strength.